Sound absorption coefficient of wet gap graded asphalt mixtures

Abstract

Acoustic absorption properties of materials have often been used to reduce the generation and propagation of sound. The research carried out in this paper deals with sound absorption in relation to road surface layers. As the presence of water affects significantly the noise generated by the tyre-road contact, an evaluation of the sound absorption coefficient was made to several wet gap-graded mixtures with different levels of porosity and different contents of rubberized asphalt bitumen. A vacuum device was used to soak the interstices of the cores with water, which were then tested by means of an impedance tube, according with standard ISO 10534-2:1998. It was found that the values of the normal incidence sound absorption coefficient became smeared over the frequency spectrum in comparison with dry samples and that the quantity of rubber in the asphalt bitumen affected the way water fills the cores and, consequently, its sound absorption characteristics.